Boiling of cellulose fibers constitutes an important operation in improving cellulose textiles. It is known that this operation, performed in an alkaline medium, eliminates foreign matter in the natural fibers and makes the fibers hydrophilic.
An attempt has often been made to improve the effectiveness of the alkaline treatment, at the same time as the saponification of the waxes and natural greases of the fibers, to increase the level of whiteness and elimination of hulls and dark colorants from the fibers and to permit a better extraction and a better elimination of inorganic materials also appearing in considerable amounts as impurities of the fibers. It has been proposed to use alkaline metal polyphosphates or aminopolycarboxylic acid salts in the alkaline boiling baths to increase particularly the extraction of the inorganic substances from the fibrous material.
The use or reducing compounds such as sodium dithionite or the salts of .alpha.-hydroxy-alkane-sulfinic acids has also been recommended in the boiling procedure to increase the degree of whiteness. It is known that if the presence of these compounds in the alkaline bath is such that no undesirable oxidation of the fiber occurs, then their effectiveness on the degree of whitening is not very great.